(1 of )Raheem Mostert, turning upfield in the Aug. 11 preseason game at Kansas City, has been the 49ers' leading rusher and third-leading receiver in the preseason.(Reed Hoffmann / Associated Press)

(2 of )Matt Barkley is scheduled to make $1.6 million this season with the 49ers if he makes the opening day roster, although that's a lot of money to pay a third-string quarterbac. (Marcio Jose Sanchez / Associated Press)

(3 of )Running back Tim Hightower came to the 49ers after having played for new coach Kyle Shanahan, but a knee injury limited his preseason production. (Marcio Jose Sanchez / Associated Press)

(4 of )Joe Williams was the 49ers' fourth-round draft choice this year but seems to have been passed on the depth chart by Raheem Mostert and Matt Breida. (Marcio Jose Sanchez / Associated Press)

(5 of )Garrett Celek's chances at making the 49ers' roster improved when the team traded Vance McDonald on Tuesday. The have only two definites at the position and will need to carry three. (John Bazemore / Associated Press)

(6 of )Kendrick Bourne has been the 49ers' second-leading receiver int he preseason and the 11th-leading receiver in the league. Cutting him would likely mean his signing with another team. (Charlie Riedel / Associated Press)

(7 of )Victor Bolden is an undrafted rookie with the 49ers, but he opened eyes with a 104-yard kickoff return touchdown. (Reed Hoffmann / Associated Press)

(8 of )John Theus is the 49ers' backup at the important left tackle position, but keeping him would mean the team probably is keeping four offensive tackles. (Jim Mone / Associated Press)

(9 of )49ers nost tackle D.J. Jones, recovering a fumble in exhibition game at Kansas City, was a sixth-round draft choice this year but is hampered by his lack of versatility. (Reed Hoffmann / Associated Press)

(10 of )Adrian Colbert has the kind of versatility team's like from the players at the bottom of their roster, and he can play cornerback, safety and special teams. (Jeff Chiu / Associated Press)

First order of business for the 49ers during tonight’s preseason game against the Chargers: Don’t play important players. The season starts a week from Sunday. Keep the starters healthy.

Second order of business: Make a list of the 45 best players on the roster, the players who definitely will make the team. These are the players the 49ers do not need to scrutinize in this game.

The box to the right my choices for the best 45 players on the roster, in no particular order.

Third order of business: Of the remaining 45 players on the 90-man roster, make a list of the guys who have legitimate chances to win one of the final eight spots on the 53-man roster. These are the “bubble players” — the players the 49ers need to evaluate most in this game.

Here’s my list of bubble players, in no particular order. And here’s where they stand before tonight’s game.

1. Matt Barkley, QB. Barkley is playing to prove the 49ers should keep him as the third quarterback. If they keep him, his $1.6 million salary for 2017 becomes guaranteed. That’s a lot of money to pay a No. 3 QB. If Barkley doesn’t play particularly well in this game, the Niners can cut him and feel confident no other team will sign him. If the Niners need Barkley later in the season, they can bring him back at a reduced rate.

2. Raheem Mostert, RB. You probably hadn’t heard of Mostert before this year — he has played for five teams during his two-season career. But during this preseason, he has been the Niners’ leading rusher (115 rushing yards), third-leading receiver (104 receiving yards) and starting kick returner. If the Niners cut him, another team almost certainly would sign him — especially if he plays well against the Chargers. Mostert has a good chance to make the Niners’ final roster.

3. Joe Williams, RB. The Niners drafted Williams in the fourth round this year presumably to be the No. 2 running back. But Mostert and Matt Breida seem to have passed Williams on the depth chart, so Williams would be the No. 4 running back if he makes the team. Typically when a team keeps a fourth running back, that player is a key special-teams contributor, which Williams is not. That doesn’t bode well for him. But, the Niners could keep Williams and make him one of their seven inactive players on game days, so they don’t have to worry about having a backup who doesn’t play special teams. Williams will need to play well against the Chargers to convince the Niners to make this accommodation for him.

4. Tim Hightower, RB. When the offseason began, Hightower seemed like a probable candidate to make the team, because he was only the running back on the roster who had played for Kyle Shanahan. Hightower’s experience in Shanahan’s running game gave him an edge. But he hurt his knee during training camp, and in the preseason he has negative 1 rushing yards. If the Niners cut him, they probably could bring him back later if they need him. It’s doubtful another team would sign him.

5. Garrett Celek, TE. After trading Vance McDonald to the Steelers, the Niners have just two tight ends who definitely will make the team — George Kittle and Logan Paulsen. Two is not enough. If one were to get hurt during a game, the Niners no longer could use any of their plays featuring two tight ends. So, the Niners need a third tight end, and Celek is the favorite to win that position. He has been playing with the starters during the preseason and he’s a good blocker, which is extremely important in Shanahan’s run-first offense.

6. Cole Hikutini, TE. The undrafted rookie caught a lot of passes during training camp. But the Niners haven’t thrown him any passes yet during the preseason games. If he gets shut out again during tonight’s game, he probably will end up on the 49ers practice squad.

7. Kendrick Bourne, WR. This undrafted rookie has been the 49ers’ second-leading receiver, and the NFL’s 11th-leading receiver during the preseason. He seems good enough to make an NFL roster. If the Niners cut him, another team may sign him. Are the Niners willing to risk losing him? They might have to keep him if he has a big game against the Chargers.

8. Victor Bolden Jr., WR. Another undrafted rookie. Bolden won’t make the team based on his ability to play wide receiver — he hasn’t caught a pass in the preseason. But he has returned a kickoff 104 yards for a touchdown. Would the 49ers keep Bolden just to return kicks? That depends on how he plays tonight.

9. John Theus, OL. Theus is the 49ers’ backup left tackle, which is an important position. But, the Niners already have three offensive tackles who probably will make the team — Joe Staley, Trent Brown and Garry Gilliam. Will the Niners keep a fourth offensive tackle?

11. Eric Magnuson, OL. Instead of keeping a fourth offensive tackle, the Niners could keep Magnuson, an undrafted rookie who plays center and guard. But Magnuson may not be a better player than Theus. Magnuson may be mere practice-squad material. He has to make a strong case for himself against the Chargers.

12. D.J. Jones, DL. Jones plays only one position — nose tackle. He’s not versatile, which hurts his chances to win one of the final roster spots. Players at the bottom of the roster have to be versatile. But, the Niners used a sixth-round pick on Jones this year — they clearly want to develop him for the future. Will they cut him and risk losing him?

13. Pita Taumoepenu, DL/LB. Taumoepenu is another rookie sixth-round pick the Niners want to develop for the future. And he plays two positions — defensive end and outside linebacker. And he plays special teams. He has a good chance to make the team.

14. Chris Jones, DL. Chris Jones is a veteran defensive linemen who played with the starters in preseason when DeForest Buckner missed time with an ankle injury. You wouldn’t think the Niners would cut someone who has played with the starters, but Jones plays only one position — defensive tackle — and he’s not someone the Niners can develop for the future. They might cut him.

15. Quinton Dial, DL. Dial is another veteran defensive lineman with a limited future. But unlike Jones, Dial plays two positions — defensive tackle and nose tackle. Dial’s versatility could help him beat out Jones for one of the final spots on the roster.

16. Adrian Colbert CB/S. Colbert is extremely versatile — he plays cornerback, safety and special teams. He is the kind of player a team wants to fill the 53rd spot on the team. But, he’s a rookie seventh-round pick. The Niners may feel they can cut him and put him on their practice squad for a year.

17. Vinnie Sunseri, S. Sunseri is a veteran, journeyman safety — not someone who figures into the Niners’ future plans. But he could help the Niners now, because he’s good on special teams. He needs to play exceptionally well on special teams tonight to make the roster.